An ion-exchange membrane method brine electrolysis is a method for producing caustic soda, chlorine, and hydrogen by the electrolyzing (electrolysis) of brine with electrodes for electrolysis. In an ion-exchange membrane method brine process, a technique that can maintain a low electrolysis voltage over a long period of time in order to cut the amount of power consumption is desired. An electrolysis voltage includes a voltage caused by resistance of an ion-exchange membrane or structural resistance of an electrolytic cell, overvoltage of an anode and a cathode, voltage caused by the distance between an anode and a cathode, or the like, in addition to a voltage that is theoretically necessary. It is known that, when electrolysis is continued for a long period of time, the voltage rises based on various reasons such as impurities in the brine.
Conventionally, electrodes called Dimension Stable (DSA) (Permelec Electrode Ltd., registered trademark) have been widely used as anodes (electrodes for electrolysis) for chlorine evolution. The DSA (registered trademark) is an insoluble electrode in which a coating of an oxide of a platinum group metal such as ruthenium is provided on a titanium substrate.
Among the platinum group metals, palladium in particular has properties of low chlorine overvoltage and high oxygen overvoltage and is therefore known as a catalyst ideal for the evolution of chlorine in an ion-exchange membrane method brine electrolysis. An electrode using palladium shows lower chlorine overvoltage than the DSA (registered trademark) and has excellent properties such as low oxygen gas concentration within chlorine gas.
As specific examples of the anode described above, Patent Literatures 1 to 3 shown below disclose an electrode for electrolysis formed of an alloy of platinum and palladium. Patent Literature 4 shown below discloses an electrode in which a coating formed of palladium oxide and platinum metal or of palladium oxide and a platinum-palladium alloy is formed by thermal decomposition on a titanium substrate. Patent Literature 5 shown below discloses a production method for an electrode where a solution in which palladium oxide powder together with a salt of a platinum compound is dispersed is applied onto a conductive substrate and then thermally decomposed. Patent Literature 6 shown below discloses an electrode in which a first coating layer formed of platinum or the like is provided on a substrate and then a second coating layer formed of palladium oxide and tin oxide is formed by thermal decomposition.